Systems of this type are known. A data bank is mentioned here as an example, whose data can be transmitted to the subscriber over a public network. A requirement for the access to the data of the data bank is that the subscriber has dialled the data bank's telephone number and his own customer number or secret number.
Due to the secret number--usually--only an authorized subscriber has access to the data of the data bank. This provides for a certain check. However, this check is not sufficient for security-sensitive data, because systematic computer-aided continuous attempts with secret numbers have already "hacked" so many a data bank and computer, as is widely known.